The invention relates to oil base well drilling and servicing fluids (completion fluids, workover fluids, sand control fluids, perforating fluids, fracturing fluids, and the like known fluids). In particular, the invention relates to all oil fluids containing a silica viscosifier which are characterized by a high low shear rate viscosity and shear thinning index.
It is well known in the oil and gas drilling and servicing art to employ fluids which exhibit an elevated low shear rate viscosity (hereinafter sometimes referred to as “LSRV”) and shear thinning index (hereinafter sometimes referred to as “STI”). See for example the following U.S. patents: Dobson, Jr. et al. U.S. Pat. No. 5,728,642 (heavy brine based fluids); Dobson, Jr. et al. U.S. Pat. No. 5,804,535 (formate brine based fluids); Brookey U.S. Pat. No. 5,881,826 (aqueous aphron-containing fluids); Dobson, Jr. et al. U.S. Pat. No. 5,942,468 (invert (water-in-oil) emulsion based fluids); House U.S. Pat. No. 5,977,030 (water-in-oil emulsions); Brookey et al. U.S. Pat. No. 6,156,708 (oil base aphron-containing fluids); and Dobson, Jr. et al. U.S. Pat. No. 6,300,286 (divalent cation-containing brine base fluids).
It is well known that certain aqueous base biopolymer-containing fluids are shear thinning, exhibiting a high low shear rate viscosity and a low high shear rate viscosity. A near zero shear rate (0.06 to 0.11 sec−1) viscosity provides a numerical value related to the ability of a fluid to suspend particles or cuttings under static conditions. Conversely, viscosity measured at shear rates above 20 sec−1 relates to the hole cleaning capacity of a fluid under annular flow conditions. Such fluids have been eminently successful for use in high angle and horizontal drilling. See for example: (1) “Drill-In Fluids Improve High-Angle Well Production”, Supplement to Petroleum Engineer International, March, 1995, p. 5-11; and (2) “Soluble Bridging Particle Drilling System Generates Successful Completions in Unconsolidated Sand Reservoirs”, J. Dobson and D. Kayga, presented at the 5th International Conference on Horizontal Well Technology, Amsterdam, The Netherlands, Jul. 14-16, 1993.
It is disclosed in Dobson, Jr. et al. U.S. Pat. No. 5,616,541 to utilize an amorphous silica as a viscosifier in calcium- and zinc-containing high density brine fluids. It is disclosed in Dobson, Jr. et al. U.S. Pat. No. 5,728,652 to provide calcium- and zinc-containing brine fluids containing one or more polysaccharide polymer viscosifiers and an amorphous silica viscosifier therein.
It is known that certain oleaginous liquids such as petroleum oils or fractions thereof, or other hydrocarbon liquids, can be viscosified or gelled by the addition thereto of certain silica viscosifiers (or thickeners). Generally an increase in efficiency of the viscosification process and a reduction in the silica concentration can be accomplished by the addition to the fluid of low molecular weight polar organic compounds which can absorb onto the surface of the silica particles forming a bridge there between.